Laterite nickel and cobalt ore deposits, or nickeliferous oxide ore deposits, generally contain oxidic type ores, limonites, and silicate type ores, saprolites, as two layers in the same deposits, separated by a transition zone. The limonitic zone includes goethite (FeOOH) and is relatively low in magnesium and nickel content. The saprolite zone includes various magnesium silicates and contains relatively higher magnesium and nickel. To minimise the equipment size for processing either the saprolites or the limonites by commercial processes, high grade limonite and saprolite are preferred. This leads to the lower grade ores and transition ores in some deposits being rejected as waste.
The high nickel and cobalt content limonite is normally commercially treated hydrometallurgicaly by a high pressure acid leach process, or by a combination of pyrometallurgical and hydrometallurgical processes, such as the Caron reduction roast-ammonium carbonate leach process.
The higher nickel content saprolites tend to be treated by a pyrometallurgical process involving roasting and electrical smelting techniques to produce ferronickel, containing generally greater than fifty percent iron together with a reject slag phase. Lower iron content metallic nickel cannot be produced by this method due to the difficulties associated with the movement of the majority of the iron into the slag, and the additional nickel losses with the increased slag quantities.
The ferronickel process is a highly energy intensive process as the ratio of total ore to nickel is typically forty to one, and most of the power is expended in melting slag. It requires a high grade saprolite source to make it economic. The power requirements and high iron to nickel ore ratio for the lower nickel content limonite, saprolite, and limonite/saprolite blends in the transition zone make this processing route too expensive for these ore types.
Accordingly, in the ferronickel process, considerable nickel ore resources, including some high grade nickel ore, are rejected to waste because of their relatively lower grade or unsuitable Si/Mg/Fe ratio for slag-making. The ferronickel process, ie RKEF process (Rotary Kiln and Electric Furnace) also has the disadvantage that the financial value of any cobalt in the ore, which reports to the ferronickel, is not realised. Moreover, the high content of iron in ferronickel restricts its end use to stainless steel production only.
The above processes generally require “whole ore” processing as there is no effective method to beneficiate the ore. This has the disadvantage that the mineralogical fractions of the ore which may contain lower metal values effectively dilute the total treated ore quality and increase recovery costs.
It would be desirable to provide a simpler, less energy intensive, and lower capital investment process to produce metallic nickel with low iron content (as herein defined), which overcomes or at least alleviates one or more of the difficulties associated with the prior art.
It would also be desirable to provide a process for producing low iron content nickel using a wide range of nickel containing ores, particularly laterite ores which are considered unexploitable by conventional processes. It would further be desirable to provide a process for producing nickel having a sufficient purity for general sale to the nickel market.
Nickel hydroxide intermediate with low or no iron content is produced as an intermediate nickel compound commercially in the Cawse Plant in Australia. In the Cawse process, lateritic nickel ore is subjected to a high pressure sulfuric acid leach to extract the nickel and cobalt, along with other impurities. Waste ore and some impurities are separated from the leachate after multi-stage neutralisation and solid/liquid separation, and a mixed nickel cobalt hydroxide is precipitated by further neutralisation with magnesium oxide.
Nickel hydroxide intermediate production by a similar process is also described in the prior art. For example, it may be produced as an intermediate from the leachate from high or atmospheric pressure acid laterite leaching or a combination of both, heap leaching of laterite or nickel sulfide ores or concentrates, or high pressure or atmospheric pressure leaching of sulfide ores or concentrates. The literature also teaches that nickel hydroxide may be produced from acidic nickel sulfate solutions produced as eluates, strip solutions, or raffinates from solvent extraction or ion exchange treatment of the prior mentioned process leachates or leach slurries.
International application PCT/AU2005/001360 in the name of BHP Billiton SSM Technology Pty Ltd discloses a process for the production of ferronickel or nickel matte by combined hydrometallurgical and pyrometallurgical processes. In the process disclosed in this specification, the nickel and iron are selectively absorbed on to a resin in an ion exchange process and thus separated from other impurities, eluted from the resin with sulfuric acid and the eluate is neutralised to precipitate a mixed nickel iron hydroxide product. The mixed nickel iron hydroxide product is then reduced directly to produce a ferronickel or nickel matte product.
In a further development of this process International Application PCT/AU2006/000225 in the name of BHP Billiton SSM Technology Pty Ltd discloses a process for the production of a high quality ferronickel product by a method which involves pelletisation of a mixed nickel iron hydroxide product, calcination to produce pellets of nickel iron oxide, and reduction of the oxide to ferronickel. Given the relatively high iron content in the calcined pellets of nickel iron oxide, the pellets are sufficiently reactive to be reduced by reaction with a gaseous reductant.
An improvement to the above processes would be to produce metallic nickel with low iron content directly from a nickel intermediate, thereby providing a higher purity nickel product.
The above discussion of documents, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention before the priority date.